1. Field of the Invention
The present general inventive concept relates to a piezoelectric inkjet head, and more particularly, to an inkjet head having piezoelectric actuators to change cross-sectional areas of restrictors, and an image forming method and apparatus having the same.
2. Description of the Related Art
An inkjet head is a device for printing a predetermined color image by ejecting minute droplets of ink on desired areas of a printing medium. Inkjet heads can be generally classified into two types according to the ejection mechanism of ink droplets. The first type is a thermal inkjet head that ejects ink droplets using the expansion force of ink bubbles created using a heat source, and the second type is a piezoelectric inkjet head that ejects inkjet droplets using a pressure created by the deformation of a piezoelectric element.
FIGS. 1 and 2 are respectively a plan view and a cross-sectional view of a configuration of a conventional piezoelectric inkjet head.
Referring to FIGS. 1 and 2, a plurality of flow channel plates 10, 20, and 30 include an ink inlet 61, a manifold 62, a plurality of restrictors 63, a plurality of pressure chambers 64, and a plurality of nozzles 65, which constitute an ink flow channel. A plurality of piezoelectric actuators 40 are formed at various positions on a first flow channel plate 10 corresponding to the pressure chambers 64. The manifold 62 is formed in a second flow channel plate 20, and performs as a common path for supplying ink to the pressure chambers 64 when the ink is supplied from an ink tank (not shown). The restrictors 63 are formed in the upper part of the second flow channel plate 20 to connect the manifold 62 to the pressure chambers 64. The pressure chambers 64 where ink to be ejected is filled are formed in the second flow channel plate 20 and arranged on one side or both sides of the manifold 62. The volume of each of the pressure chambers 64 is changed by the driving of the piezoelectric actuator 40, which causes a pressure change in the pressure chambers 64 resulting in ejecting or receiving of ink through the nozzle 65 formed on a third flow channel plate 30. For this purpose, portions of the first flow channel plate 10 that cover the pressure chambers 64 perform as vibration plates 12 that deform due to the driving of the piezoelectric actuators 40. The nozzles 65 are formed through the third flow channel plate 30 and respectively are connected to the pressure chambers 64.
An operation of the conventional piezoelectric inkjet head having the above configuration will now be described. When a driving signal is applied to the piezoelectric actuators 40, the piezoelectric actuators 40 deform together with the vibration plates 12. Thus, the volumes of the pressure chambers 64 are reduced resulting in a pressure increase in the pressure chambers 64, and thus, ink in the pressure chambers 64 is ejected to the outside through the nozzles 65. Next, when the piezoelectric actuators 40 and the vibration plates 12 are restored to the original positions, the volumes of the pressure chambers 64 are increased. Due to the reduced pressure in the pressure chambers 64, the pressure chambers 64 are refilled with ink from the manifold 62 through the restrictors 63.
However, in the conventional piezoelectric inkjet head, in the process of ejecting ink due to the driving of the piezoelectric actuators 40, the ink is ejected to the outside through the nozzles 65, and a portion of the ink backflows towards the manifold 62 through the restrictors 63.
The ink that backflows affects adjacent pressure chambers 64 through the manifold 62, that is, it causes cross-talk. The cross-talk causes unstable meniscus of ink in the nozzles 65 connected to the adjacent pressure chambers 64, and thus, causes deviations in speed and volume of ink droplets ejected through each of the nozzles 65. Also, due to the backflow of ink, the volumes of ink ejected through the nozzles 65 are reduced.
Accordingly, the restrictors 63 must function to refill ink into the pressure chambers 64 from the manifold 62 and to block the backflow of ink when ejecting the ink to the outside. In order to effectively block the backflow of ink, the restrictors 63 may have a small cross-sectional area. However, on the contrary, in order to refill ink smoothly, the restrictors 63 must have a large cross-sectional area. However, the conventional restrictors 63 have a fixed cross-sectional area, and thus, it is difficult to meet the two above conditions.